For more than a decade now we have been investigating the evolutionary history of the yellow-rumped warbler Setophaga coronata (formerly Dendroica coronata). The complex is composed of a white-throated form, Myrtle warbler in Eastern North America, and three yellow-throated forms: Audubon’s, Black-fronted and Goldman’s warblers in Western North America, Northern Mexico, and Guatemala, respectively. Early genetic studies using mitochondrial DNA revealed divergent Mexican and Guatemalan lineages relative to the closely related Myrtle and Audubon’s warblers. However, more recent work by us and collaborators Alan Brelsford and Darren Irwin (University of British Columbia) using nuclear DNA markers has revealed that shared mtDNA between Myrtle and Audubon’s warblers is the result of past introgression, and the two represent very divergent lineages when the entire genome is taken into account. Thanks to genome-wide markers we now know that all four lineages are quite distinct and likely represent different species. We have also documented interesting ecomorphological differences between the forms, driven largely by wing-shape adaptations to migratory or sedentary lifestyles.